Any idea? I thought DNA abbreviation is a big term but that’s a different, it’s a chemical terminology. But there are many apart from this. Have a look. I’m surprised those are the words never heard or seen but interesting. In terms of sheer size, however, the longest word to be found in Britain is the Welsh place name Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch. For obvious reasons, it's usually abbreviated to Llanfair PG .
Ø otorhinolaryngological - 22 letters
Ø immunoelectrophoretically - 25 letters
Ø psychophysicotherapeutics - 25 letters
Ø thyroparathyroidectomized - 25 letters
Ø pneumoencephalographically - 26 letters
Ø radioimmunoelectrophoresis - 26 letters
Ø psychoneuroendocrinological - 27 letters
Ø hepaticocholangiogastrostomy - 28 letters
Ø spectrophotofluorometrically - 28 letters
Ø pseudopseudohypoparathyroidism - 30 letters
